Added some sphinx cross-reference links to the built-in template tags and...

Added some sphinx cross-reference links to the built-in template tags and filters in multiple areas of the documentation. Also fixed a few minor inconsistencies and did a little PEP8 cleanup while I was at it.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@16922 bcc190cf-cafb-0310-a4f2-bffc1f526a37